Parts of the Hudson River stretching from New York City to Troy contain elevated levels of caffeine.

A new study from researchers at Columbia University cites the environmental concerns of caffeine and numerous other substances lurking in the river water.

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Also found in the Hudson were an artificial sweetener and numerous medications for high blood pressure, ulcers, heartburn and pain relief. The drugs likely are getting there through municipal sewer treatment systems.

"Some levels are high enough that you could be concerned about fish and other aquatic organisms," said Andrew Juhl, an aquatic biologist at Columbia University's Lamont-Doherty Earth Observatory, who coauthored the peer-reviewed study. "Right now, we don't know what the effects might be. Our point right now is to say these pharmaceuticals are there, and here's the pattern throughout the river."

Such drugs could either be passing through human bodies into sewer systems or coming directly from pills being flushed down toilets.

Researchers found varying and sometimes concerning levels of 16 different pharmaceuticals, including antibiotics, drugs for treating high blood pressure, high cholesterol, epilepsy, ulcers and heartburn, as well as the common aspirin substitute acetaminophen.

Those results were based on samples taken from more than 70 spots along the river from Troy to New York City between May and July 2016. Samples were taken from a patrol boat operated by the environmental group Riverkeeper.

The study was a collaboration with the U.S. Environmental Protection Agency, Riverkeeper, Lamont-Doherty and Queens College. It appears in the journal Water Research.

Some of the highest chemical levels were found near sewage discharge pipes for the city of Kingston, where some drugs were found in "potentially worrisome quantities." Currently, there are no federal or state regulations on safe levels of pharmaceuticals in river water.

Samples were taken in the water off the the U.S. Military Academy at West Point, which has its own sewage-treatment plant. Test results were high in May, but dropped significantly in July, when fewer students and staff were present at the academy.

The farther that samples were taken from sewer plants, the lower the levels of chemicals, likely through dilution with river water, the study also found.

Some communities use the river for a public water supply. Those systems cover about 100,000 people, and include the city and town of Poughkeepsie; the village and town of Rhinebeck; the towns of Esopus, Hyde Park and Lloyd; and the Dutchess County Water & Wastewater Authority.

Juhl said there is "no direct evidence that humans are being harmed by floating pharmaceuticals."

However, some of the drugs could harm fish or other aquatic life in the river, he added. That could include the epilepsy drug carbamazepine, which could be toxic to freshwater shrimp; the cholesterol-lowering drug gemfibrozil and the diuretic furosemide, believed to cause DNA damage in some fish; and the blood-pressure drug propranolol, which appears toxic to mussels.

"We don't know the consequences for aquatic organisms of long-term chronic exposure to any of these substances, or mixtures of them," said Juhl. "At this point, we now have some basis for concern, but we really don't know."

Earlier studies have confirmed the presence of pharmaceuticals in river waters in the Hudson and elsewhere in the U.S. Recently, researchers uncovered high concentrations of antidepressants in the brains of fish from the Niagara River in western New York.

A 1999-2000 study by the U.S. Geological Survey found measurable amounts in 80 percent of water samples taken from 30 states. A 2008 investigation by the Associated Press found detectable levels of various medications in the drinking water of some 40 million Americans.